Telephone Number Mapping A. Brown Internet Draft Nortel Networks Document: Greg Vaudreuil Lucent Technologies October 27, 2000 ENUM Service Specific Provisioning: Principles of Operation Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 1. Abstract This document outlines the principles for the operation of a telephone number directory service. This service provides for the resolution of telephone numbers into Internet domain name addresses and service specific directory discovery. Vaudreuil Expires March 2001 1 ENUM Operations Auguest 18, 2000 Table of Contents 1. Abstract........................................................1 2. Introduction....................................................2 3. Scope...........................................................2 4. Overview........................................................3 4.1 Relationship with Dynamic Services.............................3 4.2 Number Portability.............................................4 5. The ENUM Service................................................4 5.1 First Level: Determining the Delegated Authority...............4 5.2 Second Level: Determining the Service Registrar................5 5.3 Third Level: Retrieving Resource records.......................6 5.4 Service-Specific Queries.......................................6 6. Interesting Numbering Topologies...............................7 6.1 Subaddressing..................................................7 6.2 Default and Range-based Service Records........................8 7 Illustrative System Examples.....................................9 7.1 Example: Hypothetical Reachme Service..........................9 7.2 Example: SIP Call Setup Service Request.......................10 8. Security Considerations........................................11 9. References.....................................................12 10. Acknowledgments...............................................12 11. Author's Addresses............................................12 12. Full Copyright Statement......................................13 Appendix: changes from draft-ietf-enum-operations-00.txt..........14 2. Introduction This document outlines the principles for the operation of a telephone number directory service. This service provides for the resolution of telephone numbers into the address of a service specific directory or where applicable for a given service, directly into a service-specific endpoint addresses. This directory service uses the algorithms and methods described in RFC 2916. Please send comments on this document to the ENUM working group. 3. Scope This document defines the architecture and mechanics necessary to implement a telephone number-based Internet directory system. This solution enables an extensible set of services to be provided for a given telephone number. Example services may include IP telephony, store and forward or real-time Internet Fax, VPIM voice messaging, Internet paging, geographic phone location, and many others. Each service is to be separately defined and identified using a unique, registered service identifier. This document does not specify the particulars of any telephone number-based service. In particular, it does not describe how phone calls are placed, routed, or terminated or how voice, fax, pager, or email messages are routed. Vaudreuil Expires January 2001 2 ENUM Operations Auguest 18, 2000 4. Overview This telephone number-based directory system implements a four-level information model, the first two constituting the ENUM service itself. This model is based on analysis of pre-existing administrative structures, generalized service requirements, and the capabilities of candidate protocols. The mechanics of the ENUM service are specified in [ENUM] The first level is the mapping of the telephone number delegation tree to the authority to which the number has been delegated. Conceptually, this delegated authority knows nothing about service- specific information associated with the telephone number but can provide a reference to the appropriate entity that does know the specific information. The second is the delegation from the authority to which the telephone number has been delegated to the service registrar. The registrar is conceptually responsible for maintaining the set of service records for a given telephone number. Where this services registrar is different from the delegated authority, a query redirection from the delegated authority to the name server of the service registrar for a given telephone number is necessary. Because there may be multiple service providers for a given telephone number, conceptually this registrar of services assumes a role of managing service registrations and arbitrating conflicts between service providers. The third level is the set of service records themselves. The service records indicate which of several services may be available for a given telephone number. Multiple records indicating redundant or competitive service providers may be provided. The set of records may be provided or modified by any number of service providers. The ENUM service defines these records to be NAPTR records yielding a valid URL for a potentially useful service. It is up to the client initiating the service request to sort through the set of NAPTR records to determine which services are appropriate for the intended action. If necessary, an additional service-specific level of information can be provided by the service provider itself. This level provides specific attributes including any necessary attributes to place a call, route a message, validate capabilities, or other data necessary for that service that are known only by the provider of that specific service. 4.1 Relationship with Dynamic Services ED Note: Text requested discussing FAST UPDATE VS SLOW UPDATE. WG decided only slow update is in scope for ENUM. Discuss timing considerations for propagation of changed records at various levels. Illustrate how time-of-day services should be provided at the service-specific level. The telephone number delegation information changes infrequently. However, when a change to this data is made, the information must be Vaudreuil Expires January 2001 3 ENUM Operations Auguest 18, 2000 rapidly propagated through the directory system. Inconsistencies between the authoritative data and cached data may result in loss of service, misrouting of communications, and/or service loops. An effective ENUM service requires that DNS time-to-live fields be set to an appropriate value consistent with the telephone number reassignment policies 4.2 Number Portability The concept of number portability generally refers to the ability of a subscriber to change service providers, service types, or locations without changing their telephone number. For a full discussion of number portability, see [portability]. In support of number portability, the ENUM service provides mechanism at the three conceptual levels of the ENUM service. 1. If the number has been redelegated to another authority, the telephone number can be redelegated in the ENUM service to that authority by changing the name server "NS" records to point to the new authority. This may be the case where numbers are redelegated from the incumbent service provider to another or to a portability authority. The immediately higher delegated authority coordinates the transfer. 2. The service registrar may be reassigned. This may be the case where an individual or corporation changes telephony service providers and wishes that telephony service provider to also provide service registrar functions. Assuming the delegated authority and service registrar are separate entities, the DNAME or CNAME redirection records pointing to the previous service registrar would be changed to point to the new service registrar. The appropriate service specific NAPTR records would be recreated by the new service registrar and the delegated authority would coordinate the transfer from one registrar to the other. 3. If a specific service for a given telephone number was changed from one provider to another, such as switching telephone answering / voice messaging providers, the NATPR record indicating the specific service would change. The service registrar would coordinate the deletion of the record for the previous service provider and the insertion of a record for the new service provider. It is anticipated that in the early stages of an ENUM deployment, the delegated authority and the service registrar may be the same entity. 5. The ENUM Service 5.1 First Level: Determining the Delegated Authority The first level is the mapping of an E.164-formatted international telecommunication number into the identity of the service registrar for that number. This may or may not involve more than one referral in DNS. From the client's perspective, this level is transparent, bundled within the query for the service-specific resource records stored at the second level. Vaudreuil Expires January 2001 4 ENUM Operations Auguest 18, 2000 The delegation of telephone numbers from the root authority (the ITU) down to individuals is a well-established system that can be utilized. These telephone number registrars have a trusted relationship with their delegated carriers or subsidiary registrars; a valuable asset to ensure protection against various attacks. Note that in this model, the delegation of telephone number blocks or individual numbers to a corporation or to an individual can be administratively and technically modeled as a subdelegation to another carrier. With that additional information publicly registered, the mapping between telephone numbers and these domain names can be provided by any neutral entity. The delegated authority, subdelegated authority, or individual may arrange to have a third-party (e.g., a service provider) list their information. In this case the service provider's domain would be returned in the ENUM query. The Internet Domain Name System provides an ideal technology for the first-level directory due to its hierarchical structure, fast connectionless queries, and distributed administrative model. Earlier experimentation with the TPC.INT remote printing experiment has shown how the hierarchical assignment of telephone numbers can be mapped directly to the hierarchy of domains within the DNS. The ENUM directory uses that approach to map any arbitrary telephone number into a single domain name. ITU standard E.164 defines the structure of the public telephone number as follows: country code, followed by nationally significant part, followed by subaddress. The country code may be from one to three digits, and the total length may be up to 15 digits. The nationally-significant portion may be arbitrarily divided on any number boundary. In many countries numbering plans, the divisions are not uniform, that is, the "area codes" or "city codes" may be of varying lengths within a single country and the total number of digits may be variable. Where supported by the relevant service, an optional subaddress of up to four digits may be utilized to designate an extension telephone number. Note that while sub- addressing is not well supported in GSTN calling, it is more widely supported for voice messaging. It is important to note that the national long-distance access or international dialing prefix sequence is not part of the canonical E.164 number. Within this delegation flexibility, it is always the case that the delegation of authority is always done left-to-right. With this assumption, a numbering tree can be built on a digit-by-digit basis that can represent any arbitrary hierarchical structure. DNS permits the delegation of authority on arbitrary boundaries such that a delegation to country code "1", "44", and "972" can all coexist under a single numbering plan root. The same applies for "service selectors", "area codes", "city codes", "line number", or "additional address information " within numbering plans. 5.2 Second Level: Determining the Service Registrar In the event that the designated authority is not the same as the service registrar, the DNAME and CNAME records provide the redirection from the designated authority to the service registrar. The DNAME provides a means for reforming and re-issuing a query for a "non-terminal" domain name. As is standard for compliant DNS Vaudreuil Expires January 2001 5 ENUM Operations Auguest 18, 2000 resolver libraries, clients must support the CNAME record type. Servers that provide for substitution MAY support the DNAME record to provide redirection for an entire telephone number range as a DNS subtree. These servers MUST provide synthesized CNAME records for the proper operation of older resolver libraries that have not been extended to understand DNAME. Servers that redirect queries on a per-telephone number basis MUST support CNAMES. From the client's perspective, this level may be transparent based on the capabilities of the resolver library in use. The client (with the help of a suitable DNS library) must be able interpret returned CNAME and should be able to resolve DNAME records into a new domain name. The new domain name MUST be used to continue the query for the requested service records. It is important to ensure that DNS configurations provide only one path from the e164.arpa tree to a single DNS leaf-node entry. If multiple paths point to the same node, the substitution string provided in the NAPTR may provide unintended results. In particular, substitution expressions which use the original telephone number string may result in different URI's depending upon which number was used to initiate the ENUM query. 5.3 Third Level: Retrieving Resource records. The third level is the request for NAPTR RRs to discover the URL of the appropriate service-specific directory such as an LDAP directory server, H.323 gatekeeper, or specific endpoint addresses. The service registrar is responsible for ensuring that multiple services may be provided on behalf of a single telephone number, potentially by different service providers. This function includes an arbiter function to ensure that there is a deterministic instance of any given service assigned to a single telephone number. The service-specific directory locator function is a new service modeled upon existing telcoservice provisioning models. Long-distance carrier selection within the United States is one well-known example of a service-specific registration requiring an arbiter function within the current network. 5.4 Service-Specific Queries An additional level of query may be used to a service-specific directory for service-specific information. As indicated in the URI, such a query may include a SIP query to a designated gatekeeper or an LDAP query to a designated directory server. This level is specific to the service and is to be described in service-specific documents. The service-specific directory is expected to be dynamic. It is important that as little coordination as possible be required between the directories of innovative and potentially competing service-specific providers. Vaudreuil Expires January 2001 6 ENUM Operations Auguest 18, 2000 6. Interesting Numbering Topologies The following numbering uses require special consideration in the provision and use of ENUM services. 6.1 Subaddressing The E.164 standard provides for subaddressing through "additional information" within the 16 digits of an E.164 number. This information is passed through many telecommunications networks to be used by terminal equipment to select between alternate services or terminal devices. The subaddress digits are not processed by the switching system and are not used by intermediate processes to select services or route calls. In many cases, the network numbering infrastructure may be unaware of the existence or use of subaddressing by a given endpoint. Within ENUM, subaddressing may be supported in two ways. The service registrar may explicitly provision NAPTR records for each subaddress, or the service registrar may provision default records for a range of subaddresses. Using common DNS server implementations, the registrar may provision default records for a block of subaddresses. A combination of explicit entries and default entries may be provided in common DNS server implementations using a longest-match algorithm. It is important to note that if a NAPTR or any other RR is provisioned for a subaddress, then all NAPTR records that are useful for that sub- address must also be provisioned. It is also important to note that numbers with optional subaddresses may be queried without the subaddress component. For example, it may be useful to dial an address when placing a PSTN telephone call. The telephone number may terminate on an automated attendant application which can prompt for the appropriate internal extension. However, when placing a SIP call using IP telephony, the address plus the subaddress may be queried. The following set of records for company.com illustrate one configuration where a PSTN caller will be directed to the automated attendant application whether they dial the number or the number plus a subaddress, and whether the subaddress is explicitly provisioned or not. Calling using SIP to the explicitly provisioned subaddress will result in a direct call to the intended recipient. Example: 1.2.3.4.5.6.7.8.9.e164.arpa IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654321!" . IN NAPTR 10 10 "u" "sip+E2U" "!+(.*)!sip:AA@company.com!" . *.1.2.3.4.5.6.7.8.9.e164.arpa IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654321!" . IN NAPTR 10 10 "u" "sip+E2U" "!+(.*)!sip:AA@company.com!" . 1.0.1.1.2.3.4.5.6.7.8.9.e164.arpa IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:joe@company.com!" . IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654321!" . Vaudreuil Expires January 2001 7 ENUM Operations Auguest 18, 2000 6.2 Default and Range-based Service Records It is envisioned that a corporation or service provider not subject to number portability may wish to maintain a set of default NAPTR records for all E.164 telephone numbers within a delegation block. Similar to subaddressing, a service registrar may provision a set of NAPTR records for a set of E.164 numbers with similar service requirements. Example: *.3.4.5.6.7.8.9.SvcReg.company.com IN NAPTR 102 10 "u" "tel+E2U" "!+(.*)!Tel:+\1" . IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:AA@company.com!" . IN NAPTR 10 10 "U" "mailto+E2U" \ "!+(.*)!mailto:+\1@company.com!" . 1.0.3.4.5.6.7.8.9.SvcReg.company.com IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654310!" . IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:AA@company.com!" . 2.2.3.4.5.6.7.8.9.SvcReg.company.com IN NAPTR 102 10 "u" "tel+E2U" "!^.*$!tel:+987654322!" . IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:joe@company.com!" . IN NAPTR 10 10 "U" "mailto+E2U" \ "!^.*$!tel:+987654322@company.com!" . In this example, mail sent to a number within the 100's block that does not have an explicit entry will be sent to tel#@company.com. Mail is not accepted at the automated attendant number as indicted by the lack of a mailto service record. Because extension 22 has an explicit record, it must also have an explicit mailto: URL in a NAPTR record. Vaudreuil Expires January 2001 8 ENUM Operations Auguest 18, 2000 7 Illustrative System Examples 7.1 Example: Hypothetical Reachme Service The following hypothetical service enables an end-user to discover the various means by which she can reach a recipient represented by their corporate telephone number +1 613-555-1212 using the hypothetical "reachme" service. This service is hosted by directly by the recipient's corporation. The telephone number is transformed into a domain name form to be used in a DNS query. 2.1.2.1.5.5.5.6.1.3.1.e164.arpa Sample configuration file for the top level delegations from ITU: 1.e164.arpa. IN NS ns.NANP.phone.net. ;for NANP 3.3.e164.arpa. IN NS ns.FR.phone.net. ; for France 2.7.9.e164.arpa. IN NS ns.il.phone.net. ; for Israel Sample configuration file for numbers delegated from the NANP node in the DNS tree: 5.5.5.3.1.6.1.e164.arpa. IN NS ns.ServiceProviderA.net. ;for +1 613 555 XXXX In this example, ServiceProviderA.net is the authority to which the telephone number has been delegated. ServiceProviderA.net provides a non-terminal redirection pointer to Zcorporation, the designated service registrar for the block of 100 numbers +1 613 555 12XX. The configuration for this block of numbers is: 2.1.5.5.5.3.1.6.1.e164.arpa. DNAME 2.1.5.5.3.1.6.1.Zcorporation.com. Zcorporation provides the following service specific record for all telephone numbers within it's 100 number block: *.2.1.5.5.5.3.1.6.1.Zcorporation.com. IN NAPTR 100 10 "u" "ldap+E2U"\ "$!ldap://ldap1.Zcorporation.com/cn=\1!" . Assuming the resolver is using non-extended DNS, the query using telephone number +1 613 555 1212 for the _reachme service is as follows: QueryType: NAPTR QueryName: _ 2.1.2.1.5.5.5.3.1.6.1.e164.arpa. Response: IN CNAME 2.1.2.1.5.5.5.3.1.6.1.Zcorporation.com IN NAPTR 10 10 "u" "Reachme+E2U" \ "!LDAP:\\ldap1.zcorporation.com\cn=\1!" . The client can then apply the regular expression to yield an LDAP URI of LDAP:\\ldap1.zcorporation.com\cn=16135551212 and then use LDAP with the reachme schema to determine the set of communications technologies available for +1 613 555 1212. Vaudreuil Expires January 2001 9 ENUM Operations Auguest 18, 2000 7.2 Example: SIP Call Setup Service Request This example provides resolution of a telephone number to the identifier for the SIP gatekeeper designated to support real-time calling (Sipphonecall) to 972 555 1313. The telephone number is part of a block of ported telephone numbers that have been ported out of the donor carriers block to another carrier. The telephone number is transformed into a domain name form to be used in a DNS query. Sample configuration file for the top level delegations from ITU: 1.e164.arpa. IN NS ns.NANP.phone.net. ;for NANP 3.3.e164.arpa. IN NS ns.FR.phone.net. ; for France 2.7.9.e164.arpa. IN NS ns.il.phone.net. ; for Israel Sample DNS configuration file for the ported number block serviced by the 972 555 number portability authority delegated from the NANP node in the DNS tree: 5.5.5.2.7.9.1.e164.arpa. IN NS ns.972555Port.NANP.phone.net. ;for 972 555 The number portability authority manages the delegation on a per- telephone number basis. Logically, the ns.972555Port.NANP.phone.net has the following record for the telephone number. 3.1.3.1.5.5.5.2.7.9.1.e164.arpa. IN NS ns.ServiceProviderB.net. ;for 972 555 1313 ServiceProviderB provides service registrar functions directly for the telephone number and hosts the service records directly without using a DNAME record. The following configuration entry is provided for +1 972 555 1313. 3.1.3.1.5.5.2.7.9.1.ServiceProviderB.net. IN NAPTR 10 10 "u" "sip+E2U"\ "!^.*$!sip:19725551313@ServiceProviderB.net!" . The DNS Query and response using telephone number +1 972 555 1313: QueryType: NAPTR QueryName: 3.1.3.1.5.5.5.2.7.9.1.e164.arpa Result: IN NAPTR 10 10 "u" "sip+E2U" \ "!^.*$!sip:19725551313@ServiceProviderB.net!" . The client can now use the SIP protocols to contact the SIP gateway to initiate a phone call. Vaudreuil Expires January 2001 10 ENUM Operations Auguest 18, 2000 8. Security Considerations The following are known security issues taken into consideration in the definition of this directory service. 1. Service provider customer information is very sensitive, especially in this time of local phone competition. Service providers require the maximum flexibility to protect this data. 2. Registration of a domain name for the telephone numbers delegated to another carrier may result in messages being misdirected to the wrong carrier. As subdelegations are implemented, the risk that phone numbers delegated to one enterprise may be incorrectly pointed at another will increase. 3. Service providers operate in a regulated environment where certain information about subscribers must not be disclosed. Telephony services and Voice Messaging are subject to caller-ID blocking restrictions, restrictions normally enforced in the telephony network. No such protection is available on the Internet. The protection of this data is essential, but is up to the individual service providers to not disclose this information outside of their control. Vaudreuil Expires January 2001 11 ENUM Operations Auguest 18, 2000 9. References [DNS1] Mockapetris, P., "Domain names - implementation and specification", RFC1035, Nov 1987. [DNS2] Mockapetris, P., "Domain names - concepts and facilities", RFC 1034, Nov 1987. [SRV] Arnt Gulbrandsen, Paul Vixie, Levon Esibov, "A DNS RR for specifying the location of services (DNS SRV)", Work in Progress [E164] ITU, "CCITT Recommendation E.164 (1991), Telephone Network and ISDN Operation, Numbering, Routing and Mobile Service - Numbering Plan for the ISDN Era." [TPC1] Malamud, Carl, Rose, Marshall, "Principles of Operation for the TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC 1530, October 1993. [VPIM2] Vaudreuil, Greg, Parsons, Glen, "Voice Profile for Internet Mail, Version 2", RFC 2421, September 1998. [SRV] Gulbrandsen, A., Vixie, P., "A DNS RR for specifying the location of services (DNS SRV)", RFC 2052, October 1996. [REQ] Brown, Anne, "ENUM Requirements", work-in-progress, November 1999 [ENUM] Faltstrom, Patrick, "E.164 number and DNS", RFC 2916, September 2000. [DNAME] [NAPTR] M. Mealling, R. Daniel _The Naming Authority Pointer (NAPTR) DNS Resource Record_, RFC 2915, September 2000. [Portability] 10. Acknowledgments 11. Author's Addresses Anne R. Brown Nortel Networks P.O. Box 3511, Station C Ottawa, ON K1Y 4H7 Canada Phone: +1-613-765-5274 Fax: +1-613-763-2697 Email: ARBrown@NortelNetworks.com Gregory M. Vaudreuil Lucent Technologies, Communications Application Group 17080 Dallas Parkway Dallas, TX 75248-1905 United States Phone/Fax: +1-972-733-2722 Email: GregV@IEEE.org Vaudreuil Expires January 2001 12 ENUM Operations Auguest 18, 2000 12. Full Copyright Statement "Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into Vaudreuil Expires January 2001 13 ENUM Operations Auguest 18, 2000 Appendix: changes from draft-ietf-enum-operations-00.txt o Discussion of interesting numbering topologies was added o Retrieval of NAPTR records are now described in a separate step from the determination of a service registrar. o A new example was created to illustrate ENUM using sub-addressing. Vaudreuil Expires January 2001 14